How to fix Error “Allow BitLocker without a compatible TPM” error message, can’t encrypt c drive with BitLocker on Windows 10
Log on to Windows 10 computer with the account that has administrative privileges.
Go to Computer Configuration > Administrative Templates > Windows Components > Bit Locker Drive Encryption.
Select Operating System Devices.
Click Require additional authentication at startup.
Click on Enabled radio button and ensure Options section Allow Bit Locker without a compatible TPM checkbox is checked.
Click OK button to allow the changes to take effect and close Local Group Policy Editor window.